This invention relates to an antenna for aircraft and, more particularly, to an improved shunt antenna integrated to a dorsal fin of aircraft.
Shunt antennas have been used in many places over the years. Basically the term refers to antennas, which are grounded at one end and fed low voltage and high amperage radio frequencies to cause radio frequency propagation from the other end. Shunt antennas fall into this category and they have been used on aircraft vertical tail surfaces for many years. Their use on aircraft tail surfaces causes the whole tail to radiate/receive a high frequency radio signal and results in an almost equal 360 degree propagation or ability to receive a radio frequency (RF) signal.
The entire tail surface becomes a radiator/receiver of the RF signals from the antenna. The tail surfaces of the aircraft increases the surface area of the antenna and increases the propagation or ability to receive the RF signal in all directions. Prior to the advent of shunt antennas, commercial transport aircraft were equipped with “long wire” antennas whose high-speed capabilities were unacceptable, though used, on the early jets. These antennas were designed to communicate on high frequency (“HF”). A band of frequencies in the range of 2 mhz-30 mhz designated by international treaty was used for contacts over 200 miles. 2182 kilohertz is the international distress signal.
A vertical stabilizer HF shunt antenna, which covered most of the band, was developed by Eastern Air Lines (EAL). Such design is found on several Boeing aircraft today. Its failure to cover the lower frequencies is due to its shorter length, which is limited by vertical stabilizer space considerations.
Most jets now flying internationally use vertical tail mounted HF shunt antennas, with a few installations in wing root fairings, wing tip fairings and wing leading edges. If a long wire HF antenna is used it is generally installed along the length of the fuselage. The dorsal fin HF shunt antenna as designed is installed within the dorsal structure of aircraft to be installed in place of the existing aircraft dorsal. This location maximizes the signal strength both in transmit and receive modes because it uses the adjacent aircraft vertical and horizontal stabilizers as part of the shunt antenna, and the location propagates an extremely good transmit and receive signal forward and aft of the aircraft, which other HF antenna locations do not. This is also very good for radio communications because the aircrew and most ground communications are communications pertaining to where you are going or where you have been.
The antenna coupler equipment on aircraft is mounted so that it is very close to the antenna element in the dorsal. Shunt antennas work at a lower voltage and a high amperage of 75 Amps plus. This makes long feed lines from antenna coupler to antenna counter-productive due to voltage drop and the consequent power loss. Shunt antennas mounted in the vertical stabilizer mandated mounting the tuners high in the stabilizer in inaccessible or hard to access areas to accommodate this requirement. It would be advantages to mount the tuner units where they should be very close to the feed end of the antenna.
U.S. Pat. No. 6,982,677 discloses a slot antenna with an HF carrying antenna element integrated within an additional upper plate of the slot antenna. There is a further need for a shunt antenna that reserves an improved stability, efficiency and accessibility.